Found some information in my training manuals:
Introduction
The Flight Augmentation Computer (FAC) includes the following functions :
Yaw Damping
The yaw damping function enables Dutch roll damping, turn coordination in manual flight and engine failure automatic compensation.
Pitch Trim
The pitch trim function provides a means of stabilizing permanent loads on the pitch axis by modifying the trimmable horizontal stabilizer angle-of- attack.
Flight Envelope Protection
The flight envelope protection function enables to generate V min and V max signals to the FCCs, TCCs and instruments.
Maneuvering Speed Computation
The maneuvering speed computation function enables to display speed values on the speed scale (EFIS).
Configuration Data Generation
The FAC generates landing gear and flap/slat position consolidated data which are delivered to other auto flight sub-systems.
Sub-System Functions
Yaw Damper
The yaw damper system provides the following functions :
dutch roll damping,
turn coordination in low speed manual flight to reduce the sideslip induced by the turn,
automatic compensation to assist the autopilot in compensating the effects of the sideslip induced during the transient when an engine failure occurs. A command is generated to the rudder to counteract sideslip only during the transient induced by the engine failure.
Pitch Trim
The pitch trim system provides the following functions :
Electric trim
This basic function provides pitch axis stabilization and enables loads applied to the control column in manual flight to be overridden by means of the pitch trim control switches located on the control wheels.
Automatic trim or autotrim
This function which is activated at AP engagement in CMD or CWS without any action on the pitch trim control switch, permanently stabilizes the pitch axis and overcomes out-of-trim conditions :
- to enable AP operation around a zero control surface position
- to prevent jerks at AP disconnection.
Pitch stability correction
The purpose of this function is to restore static stability in that part of the flight envelope affected by a parameter :
- Mach at high Mach number = Mach trim
- Vc at high speeds = Vc trim
- angle-of-attack throughout the flight envelope = incidence trim.
ANTI STALL function
The purpose of this function is to assist the stall recovery at low speeds through a predetermined nose-down command.
Flight Envelope Protection
The FAC generates the following signals :
Envelope protection signal :
- stall warning speed (Vss). maximum selectable speed (Vmax) contingent on configuration. minimum selectable speed (Vmin) contingent on configuration
- alpha-floor signal for protection against high angle-of-attack and windshear.
This signal is used by the autothrottle for thrust correction.
Maneuvering Speed Computation
The FAC generates the following signals :
Maneuvering speed signal
- minimum flap and slat retraction speeds (V3, V4) .
- optimum maneuvering speed (Vman) contingent on configuration .
- airspeed tendency within 10s (Vc TREND).
All the speed information signals are displayed on the speed scale of the primary flight displays (PFD).
V min and V max information is used as minimum and maximum limits in certain modes related to the FCCs, TCCs and FMCs.
Configuration Data Processing
Configuration data are processed and monitored by the FAC and then transmitted to the other AFS computers via a data bus line.
These ”reliable” signals are :
- angle-of-attack signals generated from three information streams (ADC own and opposite, standby alpha probe),
- landing gear signals generated from landing gear relays and proximity detectors and
- flap and slat configuration signals generated from the SFCCs.
Hope it helps
